Acoustical apparatus



March 4, 1941. H, E OLSON EFA; 2,234,007

ACOUST I CAL APPARATUS Filed May 28, 1937 Gttorneg I Patented Mar. 4, 1941 PATENT OFFICE AC'OUSTICAL APPARATUS Harry F. Olson, Audubon, and John Preston,

Burlington, N. J.,'assig"nors to Radio Corporation of America, a corporation of Delaware Application May 28, 1937, Serial No. 145,168

7 Claims.

This invention relates to acoustical apparatus and more particularly to an acoustical diaphragm.

It has long been recognized that a direct acting diaphragm of the type used in loudspeakers,

for example, has many advantages, and it has,

therefore, been used almost universally, particularly where large output is required. For most efficient operation of a diaphragm of this sort, it is essential that it should not break up into 10 sections while vibrating, but that it should vibrate as a whole. We have found that spurious vibrations of the peripheral portions of diaphragms of this type are produced by reason of the fact that they undergo a slight twisting while vibrating.

The primary object of our invention is to provide an improved acoustical diaphragm which will be free from the aforementioned defect.

More particularly, it is an object of our invention to provide an improved acoustical diaphragm which Will not partake of spurious vibrations at the outside edge or periphery thereof.

Another object of our invention is to provide an improved acoustical diaphragm which will act more nearly like a true piston than diaphragms heretofore known.

A further object of our invention is to provide an improved acoustical diaphragm as aforesaid which is inexpensive of manufacture and highly efcient in use.

In accordance with our invention, we turn back on itself the outside edge of the diaphragm and apply a ring to the turned back edge so as to provide a relatively stiff, hollow peripheral portion for the diaphragm. The portion which is turned back may be of triangular, semi-circular, or any other desired shape, and the hollow interior may be filled with a light weight material of great strength, such as balsa wood. The usual flexible suspens-ion member is preferably cemented to the stiff annular portion and may be employed to mount the diaphragm upon a suitable support. According to another modification of our invention, the peripheral portion of the diaphragm may be turned back on itself and cemented to a hollow aluminum tube which extends around the periphery of the diaphragm. By employing a hollow section as above, the edge of the diaphragm is very rigid and stiff, and this prevents breaking up thereof, thereby eliminating spurious vibrations of its edge. Thus, the diaphragm vibrates as a whole and not in sections.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims, the invention itself, however, both as to its organization and method of operation, as well as additional obijects and advantages thereof, being best understood from the following description of several embodiments thereof, when read in connection with the accompanying drawing, in which Figure l is a central sectional view of a diaphragm formed according to our present invention, and

Figures 2 to 6, inclusive, show other modifica- 10 tions thereof.

Referring more specifically to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown, in Fig. 1, a diaphragm I made of flexible material, 15 such as paper, sized linen, a suitable synthetic resin, thin sheet metal, or the like, and of substantially frusto-conical form. The marginal portion 3 of the diaphragm I is bent away from the body portion thereof by being partly turned 20 back on the body portion in an outward direction to provide an inverted V. An annular strip 5 of suitable material (for example, of the same material as the diaphragm I) is cemented to the V-shaped, reversely bent portion in such rela- 25 tion thereto as to enclose a hollow peripheral portion which is substantially triangular in crosssection. This triangular shaped section provides a very rigid peripheral portion for the flexible body portion of the diaphragm I and prevents 30 breaking up of the diaphragm. A resilient annular suspension ring l, of rubber or the like, is cemented to the annular strip or member 5, the ring 'l extending radially outwardly from the bent-back marginal portion 3 on a radius greater 5 than that of the marginal portion 3, as clearly shown in Fig. 1, and providing means whereby the diaphragm may be mounted on a suitable baffleor the like 9, as by a plurality of bolts I I.

In Fig. 2, the marginal, reversely bent portion of the diaphragm I is made substantially semicircular in cross-section and the annular member 5 is cemented to the interior thereof, still, however, providing a stiff, hollow peripheral portion for the diaphragm I. As in the case of Fig. 1, the suspension member l is cemented to the annular member 5 and extends radially outwardly on a radius greater than that of the marginal portion 3.

In the modification of our invention shown in 5o Fig. 3, the portion 3 is completely reversely bent and cemented to the body of thel diaphragm I, thus eliminating the use of the annular strip 5. The marginal portion 3 in this case may have any suitable shape in cross-section, that illustrated 55 being somewhat of the teardrop design. Instead of cementing the suspension member 'I to the lower part of the hollow peripheral portion 3, it may be cemented to the upper part thereof, as shown in this figure.

In Fig. 4, the marginal portion 3 is similar to that shown in Fig. 2, but the annular member 5 is also made substantially semi-circular in cross-section, the member 'I being cemented to the diaphragm I between the marginal portion 3 and the annular member 5 and again extending radially outwardly on a radius greater than that of the marginal portion 3. This still provides a substantially hollow and stiff peripheral portionfor the diaphragm,. and in this case the peripheral portion is substantially circular in cross-section.

In the modification of our invention shown in Fig. 5, we employ a hollow annular tube I3 of aluminum or other light metal which is cemented directly to the reversely Abent portion 3 of the diaphragm I. The suspension ring I is also cemented to the aluminum member I3. As in the case of the modifications previously described, this construction provides a very stiff periphery or edge for the diaphragm I.

The modication of our invention shown in Fig. 6 is similar to that shown in Fig. 1, but has a ller of some strong but light material I5 therein. Examples of materials which are suitable as llers are balsa wood, pith, etc. The lightness of the material does not add substantially to the mass of the diaphragm, while its great strength and rigidity help to stiien the normally hollow peripheral portion of the diaphragm I.

From the foregoing description, it will be apparent to those skilled in the art that we have provided an improved acoustical diaphragm free from the defect previously pointed out as present in prior art diaphragms. Although we have shown and described several embodiments of our invention, it is obvious that many other modications thereof are possible, and we therefore intend that our invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

We claim as our invention:

1. An acoustical diaphragm comprising a frusto-conical member of relatively iiexible material having a body portion and a marginal portion, said marginal portion being partly turned back on said body portion outwardly thereof, an annular member secured to said frustoconical member adjacent to said body portion and to said turned-back marginal portion to cooperate therewith to enclose a hollow space and thereby provide a relatively stiff peripheral portion for the diaphragm, and flexible suspension means connected to said annular member, said suspension means extending radially outwardly from said marginal portion on a radius greater than that of said turned-back marginal portion.

2. An acoustical diaphragm according to claim l characterized in that said turned-back marginal portion and the adjacent diaphragm body portion are related to each other in the form of an inverted V in cross section, and said annular member cooperates therewith to provide a peripheral hollow portion of triangular cross-section.

3. An acoustical diaphragm according to claim l characterized in that said hollow peripheral portion is substantially semi-circular in crosssection.

4. An acoustical diaphragm according to claim l characterized in that said turned-back portion is substantially semi-circular in cross-section, characterized further in that said annular member is also substantially semi-circular in crosssection, and characterized still further in that said turned-back portion and said annular member are so associated as to provide a peripheral portion which is substantially circular in crosssection.

5. The invention set forth in claim l characterized in that said suspension means is connected to said first named member between said turnedback marginal portion and said annular member.

6, The invention set forth in claim l characterized by the addition of a filler of light-weight rigid material within said space for further stiiiening said peripheral portion.

7. The invention set forth in claim l characterized by the addition of a filler of balsa wood in said space to further stiften said peripheral portion.

HARRY F. OLSON. JOHN PRESTON. 

